JPH0714768U - Up-down converter - Google Patents

Abstract

(57) [Summary] [Purpose] To improve the frequency characteristics of NICAM audio signals. [Constitution] This up-down converter, as an output filter circuit 12, removes a signal of an adjacent channel.
Band pass filter 21, an amplifier arranged on the output side thereof, and second band pass filters 23A and 23B for matching the circuit of the latter stage. The second band pass filters 23A and 23B are A resonance circuit having a pole matched to the frequency characteristic of the NICAM voice signal is incorporated.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an up / down converter used in, for example, a cable television.

[0002]

[Prior art]

 Generally, in a cable television system, an up-down converter as shown in FIG. 4 is used to convert a cable television signal into a television signal. That is, the television signal supplied from the input end is sent to the first mixer 2 via the input filter 1 where it is mixed with the first local oscillation frequency signal from the first local oscillator 3 and becomes high. An intermediate frequency signal in a constant frequency band is provided, and this intermediate frequency signal is sent to the second mixer 9 via the bandpass filter 5, the amplifier 6 and the bandpass filter 7. The second mixer 9 mixes the second local oscillation frequency signal from the second local oscillator 10 and outputs a television signal of a constant frequency band lower than the frequency band of the intermediate frequency signal via the output filter circuit 12. can get.

[0003]

[Problems to be solved by the device]

 However, in such a configuration, the output filter circuit 12 includes a bandpass filter 21 that drops signals of adjacent channels, an amplifier 22 that receives the output of the bandpass filter 21, and increases the gain of the output signal, and this amplifier. Since it is composed of a bandpass filter 23 for receiving the output of 22 and for matching the circuit connected to the subsequent stage, when the signal of the adjacent channel is dropped by the bandpass filter 21, the lower adjacent channel Of the signals such as digital voice, NICAM sound carrier, sound carrier, and chroma carrier, which are arranged on the side closer to, the frequency characteristics of the NICAM voice signal will be worse.

[0004]

[Means for Solving the Problems] In order to solve such a problem, in the present invention, a resonance circuit is incorporated in a bandpass filter arranged at a subsequent stage of the output filter circuit.

[0005]

[Action]

 By doing this, the resonant circuit placed in the bandpass filter in the latter stage of the output circuit is coupled to the coil included in this bandpass filter, and therefore this bandpass filter has a gentle pole. , Improve the frequency characteristic of the NICAM audio signal which is deteriorated by the band pass filter characteristic of the preceding stage.

[0006]

【Example】

 Hereinafter, the details of the embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows an output filter circuit part of an up-down converter according to the present invention. The other parts of the up-down converter are basically the same as the above-described conventional configuration shown in FIG. 4, and are omitted in FIG. In FIG. 1, a bandpass filter in the latter stage of the output filter circuit 12 characterized by the present invention, that is, a bandpass filter 23A for matching with a circuit connected in the latter stage is the same as the conventional one. A coil L1 and a capacitor C1 connected in parallel with the coil L1 and having one end grounded are provided. A resonance circuit LC including a coil L3 and a capacitor C3 is further provided, and the coil L3 is arranged so as to be inductively coupled with the coil L1. In this case, one end of the resonance circuit LC is also grounded.

In the configuration of the present invention as described above, since the resonance circuit LC is inductively coupled to the coil L1, the resonance circuit LC provides a gentle pole in the frequency characteristic of the output filter circuit 12, and the NICAM audio signal The frequency characteristic can be improved.

2A, 2B, and 2C are comparison diagrams of the frequency characteristic of the NICAM audio signal of the above-described embodiment and the conventional frequency characteristic, and the conventional output filter circuit 23 is It has the frequency characteristics as shown in FIG. 2 (a), and the signal of the adjacent channel is removed by this, but in this circuit configuration, the NICAM voice signal centered on the NICAM carrier is As shown enlarged in b), the level difference between the left and right signals centering on the carrier is large. On the other hand, according to the present invention, by providing the pole by the resonance circuit LC, as shown in FIG. 2C, a gentle pole is formed around the NICAM carrier, and the NICAM carrier is centered. It is understood that the level difference between the left and right signals is significantly improved compared to the conventional method.

FIG. 3 shows another embodiment of the present invention, and the same elements as those in FIG. 1 are designated by the same reference numerals. In the figure, in the bandpass filter 23B, a series body of a coil L2 and a capacitor C2 is inserted into the output side of the amplifier 22, and a capacitor C3 and a coil L3 are connected in parallel between the capacitor C2 and the ground. A series body of the resonance circuit LC and the capacitor C4 is connected. Also in this case, the coil L3 and the coil L1 of the resonance circuit LC are inductively coupled.

Even with such a configuration, the poles can be provided as in the above-described embodiment, and the same effect can be obtained.

[0011]

[Effect of device]

 As is clear from the above description, when the up-down converter according to the present invention is used, a gentle pole is formed centering on the NICAM carrier, which can significantly improve the frequency characteristic of the NICAM voice signal. .

[Brief description of drawings]

FIG. 1 is an output filter circuit diagram of an up / down counter according to a first embodiment of the present invention.

2A, 2B, and 2C are characteristic diagrams for explaining the operation of FIG. 1 in comparison with a conventional one.

FIG. 3 is an output filter circuit diagram according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram of a conventional up-down converter.

[Explanation of symbols]

1 Input Filter Circuit 2 1st Mixer 3 1st Local Oscillator 5, 7, 21, 23, 23A, 23B Bandpass Filter 6, 22 Amplifier 9 2nd Mixer 10 2nd Local Oscillator 12 Output Filter Circuit L1, L2 L3 coil C1, C2, C3, C4 capacitor

Claims (1)

[Scope of utility model registration request] 1. An up-down converter for converting a supplied cable television signal into a television signal through a frequency conversion means and an output filter circuit, wherein the output filter circuit removes an adjacent channel signal. A filter, an amplifier arranged on the output side, and a second bandpass filter for matching with a circuit in the subsequent stage are provided, and the second bandpass filter is a pole matched to the frequency characteristic of the NICAM audio signal. An up-down converter having a built-in resonance circuit having a.